The invention relates to a two-way seat-type valve having a valve seat which is arranged between a first and a second connection, and having a closure element which co-operates with the valve seat, is arranged in a guide so as to be movable towards the valve seat or away from the valve seat, and is subjected to a control pressure prevailing in a pressure chamber on the side, remote from the valve seat, of the closure element.
Valves of this type are used as hydraulic valves for controlling fluid flow and fluid pressures. They function without any problem, as long as oil, especially a synthetic hydraulic oil, is used as hydraulic fluid.
For some time, however, attempts have been made to replace the hydraulic oils, especially the synthetic hydraulic oils, by means of water, because of their somewhat questionable properties, from the environmental point of view, and especially of their toxicity. However, water has practically no lubricating properties, and, moreover, in many cases leads to corrosion damage, so that valves of this type wear out relatively quickly, or even seize up, so that they can no longer fulfil their function or can no longer do so to a satisfactory degree.
In the case of a valve of the type mentioned initially (DE 36 37 208 C2), it was therefore proposed to prevent the closure element from coming into contact with the guide by guiding the closure element in the guide by means of guide rings. The gap thereby produced between the closure element and the guide is closed by an additionally provided sealing element. A construction of this type, however, has the drawback that the opening and closing times become longer. The reaction characteristics of the valve therefore become poorer. This excludes the use of such a valve in applications in which it is a question of similar reaction times to those occurring when using oil as hydraulic fluid.